MCB 100 1st Edition Lecture 26 Outline of Last Lecture I. Antibiotics that inhibit peptidoglycan biosynthesis II. Antibiotics that inhibit protein synthesis by bacterial ribosomesIII. Mechanisms of resistance to antibiotics seen in some bacteriaIV. Minimum inhibitory concentration (MIC)V. Therapeutic Index (T.I)VI. Antifungal, antihelminthic, and antiprotozoan drugs VII. Antiviral drugsOutline of Current Lecture I. Applied microbiology- Food preservationII. Ancient techniques that aid in food preservationIII. Modern techniques that aid in food preservationIV. Food spoilageV. Commercial sterilization vs. biological sterilizationVI. Four steps in commercial canningVII. Three types of canned food spoilage caused by thermoduric anaerobesVIII. FreezingIX. DehydrationX. Chemical preservatives to prevent food spoilageXI. Milk microbiologyXII. PasteurizationXIII. Cheese and yogurt productionXIV. Beer productionXV. Water treatmentCurrent LectureI. Applied microbiology- Food preservationa. Food spoilage can cause a great economic loss and undesirable microbial growth can cause food poisoningb. Food preservation predates the science of microbiologyII. Ancient techniques that aid in food preservationa. Salted, smoked, or dried meat lasts longer than fresh meatb. Keeping food in a cool place slows spoilagec. Souring helps to preserve foodsII. Modern techniques that aid in food preservationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Sanitary handling: clean plant, frequently sanitized equipment, clean hands, uniforms and hairnets, insect and rodent control reduces food contaminationb. Rapid automated packaging that immediately follows cooking c. Improved sorting proceduresd. Pasteurizatione. Chemical preservatives II. Food spoilagea. Causes: i. animals- often small invertebrates such as insects, snails, and worms ii. Microbial growth- damage to food, toxin productioniii. Environmental factors- oxidation, drying, moisture, dirt/dustiv. Ripening enzymes- some fruits and vegetables will "self destruct" b. Primary vs. secondary food spoilagei. Primary spoilage occurs in the field and is usually caused by insect infestations or moldy products. Buyers and sorters usually deal with this problem by discarding adulterated commodities 1. Ex. Moldy tomatoes may be thrown away rather than used to make ketchup ii. Secondary spoilage occurs in the food processing plant or later1. Ex. Botulism grows in improperly canned food and toxins are produced while the food item is being stored. Modern commercial canning procedures are primarily designed to kill botulism spores. Botulism sporesare super tough. Any procedure that effectively kills them kills all other bacteria that commonly cause food poisoning II. Commercial sterilization vs. biological sterilization a. Biological sterilization means eliminating all living organisms from a given sample or environmentb. Commercial sterilization means freedom from Clostridium botulinumc. The goal of commercial canning procedures is to ensure that a food product is free ofthe endospores from clostridium botulinum, not necessarily free of all microbial life d. Clostridium botulinum is important because:i. It produces an extremely potent neurotoxin ii. Grows anaerobically at room temperatureiii. Is fairly common in the soiliv. Produces endospores that are very resistant to heat- a process that kills clostridium botulinum endospores will kill most microorganisms v. (thermophillic bacteria that are more heat resistant than clostridium are usually not a problem in food preservation because they don’t grow at room temperature) II. Four steps in commercial canning a. Blanching: exposure of food to steam or hot water softens food, sets the color, removes gummy substances and inactivates enzymes in the food that cause it to "self-destruct" when stored. Blanching kills some microorganisms but that isn't the main goalb. Exhausting: removal of oxygen, creating anaerobic conditions. This gets rid of or prevents growth of aerobic microorganisms c. Processing: exposing the product to temperatures above 100 degrees C in a retort (a pressure cooker or autoclave). The amount of time and temperature of this step is influenced by the water content of the product and pH. General goal is to use minimal amount of heat needed to kill all Clostridium botulinum spores. An acidic pH reduces heat resistance of most bacteria so foods with a low pH require less processing time than foods with a neutral pH d. The canned product is cooled rapidly to prevent the growth of any thermophiles thatmay have survived the processing and to stop the heat from causing the product to be overcooked II. Primary types of canned food spoilage caused by thermoduric anaerobes (3 types): a. Flat-sour spoilage: can doesn’t bulge, acids build up in product. Usually caused by bacteria in the genus bacillus that convert sugars to organic acids such as lactic acidb. Swells: ends of the can bulge due to build up of gases such as CO2 and H2 that are produced as fermentative waste products by clostridium species c. Sulfide- stinkers- caused by a clostridium species that makes H2S gas in the can. The can might not swell because H2S is soluble in water. The H2S can react with iron ions from the product or the can and produce a black precipitate of FeS II. Freezinga. Retards growth of microorganisms and so prevents spoilage, but freezing does not kill most bacteriab. Its important to cook or consume frozen foods soon after they are thawed II. Dehydrationa. Removal of waterb. Bacteria cannot grow in a medium with a low water activityc. Drying meat and fruit is a very old way of slowing spoilage d. Ex. Beef jerky, raisins, powdered milk, powdered eggse. Products are stable at room temperature for long periods of timef. Wide variety of foods can be preserved by freeze dryingg. Two common problems associated with dehydrated foods:i. Safe clean water is needed to rehydrate the foodii. Some powdered foods may be difficult to dissolve II. Chemical preservatives to prevent food spoilagea. Various chemicals that prevent the growth of microorganisms can be added to foods as long as these chemicals:i. Pose no danger to the consumerii. Do not damage taste of productb. High concentrations of salt and sugar can inhibit microbial growth by reducing the water activity of the foodc. Some herbs naturally contain substances